PreToolUse Hook - Claude Code
Fires before any tool executes. Allow, deny, defer, or modify the call.
PreToolUse is the most powerful hook point. Every tool call flows through it, and the hook can allow, deny, defer, or rewrite the call before it executes.
What it does
The hook receives the tool name and arguments. Return values drive decision: allow the call as-is, deny with a reason, defer (ask the user), or modify (adjust arguments before execution). This is the extension point for custom policy engines, dynamic rewriting, and fine-grained safety controls.
When to use it
- Enforcing "no Bash commands from this list" policies.
- Rewriting edits to match house style automatically.
- Auditing every tool call to an external system.
- Deferring specific calls to a human reviewer even in auto mode.
Gotchas
- Every tool call pays the hook's latency cost. Keep the hook fast.
- Modifying arguments without telling the user can cause confusion. Log changes clearly.
- A bad hook can block every tool call and wedge the session. Test in a throwaway session first.
Official docs: https://code.claude.com/docs/en/hooks.md#pretooluse
Technical content at the intersection of AI and development. Building with AI agents, Claude Code, and modern dev tools - then showing you exactly how it works.
Was this helpful?
Related Guides
Related Tools
Claude Agent SDK
Anthropic's SDK for building agents on the same tools, agent loop, and context management that power Claude Code. Python...
View Tool
Claude Code
Anthropic's agentic coding CLI. Runs in your terminal, edits files autonomously, spawns sub-agents, and maintains memory...
View ToolCodeburn
Interactive TUI dashboard that shows exactly where your Claude Code and Cursor tokens are going, in real time.
View ToolConductor
Mac app for running parallel Claude Code, Codex, and Cursor agents in isolated workspaces. Watch every agent work at onc...
View ToolRelated Videos
Generate Videos in Codex + Claude Code with This...
Check out HeyGen! https://heygen.1stcollab.com/developersdigest The video introduces HeyGen, an AI video generation platform with a rich API and a CLI that lets developers create, fetch, and manipula...
10x Design in Claude Code and Codex
Try Higgsfield: https://higgsfield.ai/s/higgsfield-general-campaign-developersdigest-juDMTi AI coding agents can build entire websites in minutes, but the default results often still look generic and...
Self Improving Applications with Claude Code & Codex
Build a Self‑Improving Next.js App: Supabase + Vercel Eve + GitHub Issues + Agent Loops Check out Supabase: https://supabase.plug.dev/1wWOTGS The video demonstrates how to build and deploy a self-im...
Related Posts
Claude Fable 5.1 in Claude Code: How to Switch, Pin, and Pay Less
Claude Code v2.1.257 points /model fable at Fable 5.1: 1M context, $10/$50 per MTok, $0.25 cache reads. Setup, gotchas,...
Claude Design, Slides and Docs in Any Chat: How to Use Them
Claude Design, Slides and Docs now open in any Claude chat, Claude Code session or the Artifacts tab, on every plan. Exa...
Claude for Startups Offer Paused: What Founders Do Now
Claude for Startups paused its free Claude Team year and $1,000 API credit offer at capacity. What the program page says...
Claude Advisor Tool vs a Bigger Model: When the Pairing Pays
Anthropic's own runs: a Fable 5.1 advisor added 1.7 points to Opus 5.5 for 2.1x the cost. When the Claude advisor tool p...
Claude Code Retry Watchdog: Keep Unattended Runs Alive
CLAUDE_CODE_RETRY_WATCHDOG=1 makes Claude Code wait out 429 and 529 errors instead of failing after 10 retries. When to...
Claude Max API Credits: $100 a Month, What They Cover
Claude Max and Team plans now include a monthly Claude API credit, starting at $100 on Max 5x. What it covers, what it d...
